The use of endoscopes for diagnostic and therapeutic indications is rapidly expanding. To improve performance, specialized endoscopes have been developed for specific uses. For example, there are upper endoscopes for examination of the esophagus, stomach, and duodenum, colonoscopes for examining the colon, angioscopes for examining blood vessels, bronchoscopes for examining the bronchia, laparoscopes for examining the peritoneal cavity, and arthroscopes for examining joint spaces. The discussion which follows applies to all of these types of endoscopes and any modifications thereof.
There has been a large increase in the use of endoscopes for screening symptomatic and asymptomatic patients. These endoscopes are expensive and are used in contaminated and sensitive environments. Conventional endoscopes typically have an elongated insertion tube that is inserted into a patient at a point of entry and extended to a selected body cavity. The insertion tube is connected at its proximal end to a handle portion. The distal end of the insertion tube is controlled and steered by control cables that are attached to the insertion tube's distal end and extend the length of the insertion tube. The control cables are directly connected to control wheels mounted to the handle portion. The control wheels are used to control articulation of the insertion tube by rotating the control wheels relative to the handle, thereby pulling directly on the control cables and causing the distal section of the insertion tube to bend. Accordingly, the insertion tube can be steered by a physician to follow the contours of a pathway through the patient's body to desired body cavity. The tip of the insertion tube must be accurately steerable in the up/down and left/right directions to permit the physician to place the tip at a selected location once the distal end of the insertion tube is within the selected body cavity.
The insertion tube of a conventional, non-sheathed endoscope includes a biopsy channel, suction channels, and air and water channels that extend along the length of the insertion tube. The insertion tube is axially rigid, yet sufficiently flexible to allow it to follow the curves and bends along the pathway in the patient; however, it must be sufficiently stiff in order to prevent the biopsy channel, the suction channel, or the air and water channels from collapsing when the insertion tube is articulated.
Improved endoscopes are used with an endoscopic sheath, as is described in U.S. Pat. No. 4,646,722, to Silverstein et al. The sheath covers and isolates the insertion tube from the contaminated environment. The sheath typically includes a plurality of integral channels, including a biopsy channel, a suction channel, and air and water channels. The endoscope sheath is sufficiently flexible to bend with the insertion tube while being stiff enough to prevent the channels from kinking or collapsing during articulation of the insertion tube.
It is especially important that the biopsy channel of the insertion tube or sheath not collapse or excessively narrow because an endoscopic accessory, such as a forceps or the like may be required to travel along the biopsy channel during an endoscopic procedure, or alternatively, it may be necessary to remove particulate matter from the tip of the endoscope through the biopsy channel. In addition, the endoscopic accessories further add to the overall stiffness of the sheathed or unsheathed insertion tube.
The necessary stiffness of the unsheathed or sheathed insertion tube results in a significant resistance to articulation of the insertion tube's distal end that is felt by the physician during manipulation of the control wheels. The resistance to articulation is overcome by exerting a significant amount of axial force on the selected control cables. Accordingly, a significant amount of force must be exerted by the physician on the conventional control wheels so as to sufficiently pull on one or more of the control cables to overcome the inherent resistance to bending.
During a clinical procedure the handle portion of the instrument is typically held in the physician's left hand. The right hand is usually placed on the endoscope's shaft to advance the instrument into the patient and to retract the instrument out of the patient. Preferably, the physician's right hand is not used to manipulate the control wheels in order to avoid contamination of the endoscope. Accordingly, the control wheels are adjusted with only one hand. The physical effort required to rotate the control wheels with one hand to overcome the stiffness of the insertion tube, sheath, and accessory can result in excessive fatigue of the physician's left hand, particularly during a long endoscopic procedure. The excessive effort required to articulate the insertion tube also greatly increases the duration of a procedure, thereby reducing the cost efficiency of the endoscopic procedure.
Conventional endoscopes have been designed to reduce the amount of effort required to move the control wheels by rigidly connecting a small diameter drum located within the handle portion to a large diameter control wheel that is rotated by the physician's thumb. The control cables extend around the small diameter drum so as to move axially when the drum is rotated. Although the combination of the large control wheel and smaller drum facilitates articulation of the insertion tube's distal end, the optimum size combination of control wheel and drum still requires a substantially large force to be exerted by the physician on the control wheels to achieve the necessary torque on the drum to steer or otherwise control the insertion tube's distal end.
There are other endoscopic devices which require the generation of a force at the distal tip of the device. A lithotripter is a basket device which is used to crush kidney or bile stones for removal. A conventional lithotripsy device uses a screw mechanism that is rotated at its proximal end in order to provide sufficient force at the distal end to crush the stones and facilitate their removal. The force required to turn the screw to generate the sufficient force to crush the kidney or bile stones is typically high enough that it is very difficult for the physician to maintain during the endoscopic procedure without mechanical advantage.